plompzakken is a dutch sex act where the woman where's a belt around her waist which she pulls tight. After which the vagina spreads open very wide and the man is able to put both his cock and his balls inside her.
Accidents have happened during plompzakken, where the belt snapped and the man is trapped with his dick and scrotum inside the woman. This is, needless to say, very tight, and not without pain.